5 replies to this topic

[m1n1]

My car has not been on the road since 2011.   It will be soon! i rebuilt the engine last year and trying to trace a vacuum leak.. i suspect its the 24 year old stage 1 kit inlet manifold not being flat anymore.. anyhow the idle is up and down, slowly hunting.   

 

-- on my hif44 if i put my finger on the vent tube it stalls immediately and if i spray brake cleaner down it the rpm rises.   As its a 'vent' tube this should be venting to atmosphere only?   

 

 

- also on the look out for a large bore inlet manifold to match the ports in the big valve head!   is the maniflow one the only one available? 

[GraemeC]

Which do you call the vent tube?

Do you mean the one that comes out horizontally that the crankcase breathers usually connect to? If so then what you describe sounds normal - the carb needs to be tuned to suit how that tube is, or isn’t, connected.

The alloy inlet manifolds can usually be ported to match the head.

[KTS]

..the only 'vent' tube apart from the fuel overflow would be the inlet for the crankcase breathers which should not be open to atmosphere.

Chances are you've got the mixture set so rich to compensate for the air coming in through that open port that when you block it off it dies because it's over rich

[m1n1]

I meant fuel overflow tube (its called vent tube in my rebuild book)  Not the breather tube which is the big one but the small bore one.  DSC_2432.jpg   54.1K   0 downloads

[KTS]

Yes; that one vents to atmosphere

[Ethel]

It's a vital bit of what makes the carb work.

 

Air flowing through the venturi creates low pressure over the jet. The vent lets atmospheric pressure in to the float chamber & it pushes fuel up the jet in to that low pressure - like a U tube barometer.